[Limbus Company] Sunshower Heathcliff vs. 6-34

4 days of on-and-off grinding... probably 800+ resets... I finally got it today.

As far as I know, I'm the 3rd person to do this solo,    / @ripkully3465   and    / @귀찮은사람   did it first.

First and foremost, for the people that don't know, the boss has 3 shield phases:
Explosive Wrath: Every time he gets hit he gains 1 OFF LV UP and 1 DEF LV DOWN next turn (up to 9 times)
Explosive Gloom: Every time he gets hit, lowers the attacker's SP by 3, boss gains 1 OFF LV UP next turn and 1 Sinking Count (up to 9 times)
Explosive Envy: Every time he gets hit, inflict 2 bleed and 2 bleed count on the attack, boss gains 1 DEF LV DOWN next turn (up to 9 times)

Break down of the strategy is:
Turn 1: Be faster than the boss and lose clash against Smackdown with Umbrella Thwack. Leads to less damage than normal and SP loss for later
Turn 2: Be faster than the boss and lose clash against a Bat Bash with Umbrella Thwack, this will lock you at -45 SP so you can clash and win against Smackdown with Puddle Stomp. Also check what skill slot the boss' Guard is targeting, if it targets the skill slot with Puddle Stomp that means it will defend it and will lead to less damage, if it targets the skill slot with Umbrella Thwack that mean his defend will not be used at all.
Turn 3: Corrode into TS4 Telepole, get 3 corroded skills and clash 3 of bosses attacks, preferably 2 Smackdowns and 1 Bat Bash.
This is where the run starts to differ.
Turn 4: Should be very close to staggering the boss, go full damage on him. If you can avoid clashing, avoid it.
Turn 5: Boss is staggered, bring his HP closer to the next threshold.
Turn 6: Boss is in Explosive Gloom Phase. Be faster than the boss. If you clashed on turn 4, that means you can't bring your SP down to -45 yet, try to stagger the boss but not bring his HP below 905, that will trigger the Explosive Envy Phase.
Turn 7 (Skip if you got to -45 SP): Boss should be staggered and not in Explosive Envy phase yet, bring him to 905 HP and try to get any resources you might need for a passive.
Turn 8: Should be corroded into Telepole again. Depending on how many corroded skills you get, you can kill here. Clash as many attacks as you can. 4 corroded Telepoles should be enough to stagger the boss at the very least.
Turn 9: If you didn't kill yet, you should've staggered the boss, if not, ouch. If the boss is close enough to dying and you're relatively healthy, like 40+ HP, go for the win. If not, don't do anything, don't attack, just use counters.
Turn 10: Hopefully you don't die in 1 hit from the boss' counter. If you're faster than the boss, go for the kill without clashing. If you're slower, clash his attacks and you should win here.

Notable Support Passives:
W Don (More damage, especially for turn 4, if you get 3 Puddle Stomps)
LCCB Rodion (if you can trigger it by turn 8, you only need 3 Corroded Telepoles to stagger the boss, like in the video)
G Corp Outis (Can help you deal more damage on turn 8, if you trigger it)
Reindeer Ishmael (Helps with damage through turn 5-7)
Mariachi Sinclair (Can only really trigger on turn 10, if you get to that point)
LCB Gregor (Heals you 5 HP every turn from 4 onwards, very good)

First day I was trying to corrode on turn 4, which was very hard and rng-reliant to do because it involved breaking 2 coins during clashing and still losing the clash. It was annoying me more and more every time it didn't happen, so I gave up for a day. Next day I was RIP Kully streaming his attempts, staying in chat for a while, noticed that his turn 1-4 strat was way more straight forward and decided to adopt it and continue my attempts. Fast-forward like 600 attempts and I got it today.

I had a lot of close attempts before this one. Most heartbreaking one I had was when I actually killed the boss but at the same time I died to bleed, so it counted as a loss. Had multiple ones that died to speed RNG on Explosive Envy phase, I had 5 Telepole Corrosions, couldn't clash the boss' 4 coin skill and died to rupture, couldn't stagger him in time either. Another attempt I left the boss at 84 HP with Explosive Envy activate, and I had 4 HP, couldn't kill the boss in 2 hits to not die to bleed...

Timestaps:
0:00 - GODcliff
4:26 - Cutscene
5:17 - Result Screen

Music used:
   • Limbus Company OST - Canto VI Boss 1 Battl...  
   • Limbus Company OST - Canto VI Boss 2 Battl...